The present invention concerns a method for locating weft thread defects in a fabric. This method can be put into practice, for example, in a weaving loom immediately after the weaving of the fabric or at a special check point independently of the weaving loom.
More particularly, the invention concerns a method for quantifying a value corresponding to the fabric quality and more particularly the relative location of the weft threads.
It is known that defects can occur in fabrics as a consequence of improper positioning of the weft threads during weaving. Generally speaking, these defects are related to the starting strips which are formed due to the fabric being more open or tight at various locations than what is normal. Relaxation starting strips can also occur if one or several weft threads are located at a position that is too deep if, for example, one weft thread is inserted into the fabric with excessive tension.
It is known that, in order to track down such defects at the weaving loom and more specifically, to locate variations of fabric density resulting from such defects, methods can be used that enable rapid adjustment of the weaving process. According to U.S. Pat. No. 4,582,095 such a check is carried out at the weaving loom by using a close up lens and a video camera to generate an image of the fabric, following which the image is digitized by the use of a matrix (i.e., a computer pattern recogntion system)and the distance between weft threads is calculated from this information.
This known method has, however, the disadvantage that fabrics without a contrasting profile cannot be checked simply by using this technique. Indeed, in the case of fabrics with a large fabric density and also in the case of fibrous fabrics, the edges of the weft threads are difficult to distinguish and it is consequently quite impossible to carry out an automatic check in a relatively simple way.